1. Field of the Invention
The present invention relates to a molded case circuit breaker (abbreviated as MCCB hereinafter) and, more particularly, to a large capacity movable contactor assembly for a current limiting type MCCB having a plurality of contacts for each phase (pole).
2. Description of the Related Art
In general, a MCCB is an electric device for protecting an electrical load and an electric circuit by breaking a fault current, such as an overcurrent, an instantaneous large current, or a short-circuit current that occurs in the electric circuit between an electric power source and the electrical load.
In particular, a large capacity MCCB is largely used as electric power distribution equipment for protecting a circuit and a load device against a fault current in a large capacity electric power consuming locality such as a building, a factory, and the like.
A current limiting type MCCB, among the foregoing MCCBs, includes a stationary contactor having a bent shape, such as a “U” shape, so the direction in which current flowing through the stationary contactor and the direction in which current flows through the movable contactor are the opposite. In the current limiting type MCCB, when a fault current occurs, a current limiting operation is performed such that a movable contactor is separated from the fixed contactor by an electromagnetic repulsive force between the movable contactor and the fixed contactor whose currents flow in the opposite direction, before an interlocking operation between a trip mechanism which detects the generated fault current and a switching mechanism for driving the movable contactor such that the movable contactor is separated, namely, tripped, from the fixed contactor by a trigger of the trip mechanism.
Because the large capacity current limiting type MCCB has a large current capacity, a plurality of movable contacts and fixed contactors are installed for each phase of the electric circuit connected to the MCCB, e.g., three-phases alternating current circuit, so that current can dividedly flow through the plurality of movable contactors and fixed contactors.
The present invention relates to a movable contactor assembly for such a large capacity current limiting type MCCB. An example of a movable contactor assembly for a large capacity current limiting type MCCB according to the related art will now be described with reference to FIGS. 1 to 3.
FIG. 1 is an perspective view showing the configuration of the movable contactor assembly for the current limiting type MCCB according to the related art. FIG. 2 is a perspective view showing an internal configuration of the movable contactor assembly without a holder and a spring holder in FIG. 1. FIG. 3 is a front view of the movable contactor assembly of FIG. 1.
As illustrated, the movable contactor assembly for the current limiting type MCCB according to the related art includes a terminal base 18, a movable contactor 11, a holder 12, a spring holder 13, a catch 16, spring support pins 15, and springs 14.
The terminal base 18, which is provided for each phase (in other words each pole) of an AC circuit to which the MCCB is connected, is a conductive member electrically connected to the movable contactor 11. The terminal base 18 is fixedly installed at a case (in other words at an enclosure) of the MCCB, and electrically connected to an external electric power source or an electric load. As shown in FIG. 3, the terminal base 18 includes an extended portion 18a which extends from the terminal base 18 and is brought into contact so as to be electrically connected to the movable contactor 11.
A plurality of movable contactors 11 are provided for each of the phases (poles) of the AC circuit to which the MCCB is connected. The movable contactors 11 are connected with the terminal base 18 by the means of connection pins (no reference number given) and rotatable centering around the connection pins. When a portion where a contact is positioned in the movable contactor 11 is a front portion, a contact surface 11a contacted by a roller 17 (to be described) when the movable contactors 11 is rotated in the current limiting operation is a front portion, the opposite side of the front side, namely, an outer circumferential surface of the rear end portion (refer to reference numeral 11b in FIG. 3), is configured to include a slant surface portion and curved surface portion.
The holder 12 is coaxially connected to the terminal base 18 together with the movable contactors 11 by the connection pins. The holder 12 is rotated, along with the movable contactors 11, to a circuit opening position or a circuit closing position upon receiving a switching driving force from a switching mechanism (not shown) for switching the movable contactors 11 through a link.
The spring holder 13 is fixedly connected to the holder 12, and supports one end portion of each of the spring support pins 15. With reference to FIG. 1, the spring holder 13 includes a plurality of pin through holes allowing one end portion of each of the spring support pins 15 to pass therethrough.
The catch 16 is fixedly coupled to the terminal base 18 and positioned in a rotation path of the movable contactors 11 to limit the rotation range of the movable contactors 11.
As shown in FIGS. 1 and 2, a plurality of spring support pins 15 are provided for each of the phases (poles) of the AC circuit to which the MCCB is connected, and each of the spring pins 15 has one end portion extending through the pin through hole and the other end extending toward the movable contactor 11. Each of the spring support pins 15 is a member having a rod-shape. One end portion of each of the spring support pins 15 is pointy, and a spring seat portion for supporting the springs 14 and the rotatably supported roller 17 are provided at the other end of each of the spring support pins 15. Each of the spring support pins 15 can be linearly movable according to a position at which the roller 17 comes into contact with the contact surface 11a of the movable contactor, and accordingly, the pointy one end portion of each of the spring support pins 15 can be linearly movable through the pin through hole of the spring holder 13.
Each of the springs 14 is configured as a coil spring and is disposed to cover an outer circumferential surface of the sprig support pins 15. When a current limiting operation is performed, the roller 17 is brought into contact with the contact surface 11a of the movable contactor 11 according to the rotation of the movable contactor 11. Namely, in FIG. 2, when the roller 17 comes into contact with a lower end of the slant surface portion and the curved surface portion of the contact face 11a, the spring 14 extends to provide a moment to the movable contactor 11 for the movable contactor 11 to rotate counterclockwise (here, the counterclockwise direction is a direction in which the movable contactor 11 is brought into contact with a not shown fixed contactor). As the roller 17 approaches an upper end of the slant surface portion of the contact face 11a, the spring 14 is compressed to reduce the moment applied to the movable contactor 11
FIG. 3 shows a case in which three movable contactors 11 are installed for each phase of the AC circuit to which the MCCB is connected, and the three movable contactors 11 have a rear end portion 11b, respectively. The terminal base 18 has a plurality of extending portions 18a formed to be spaced apart by a predetermined distance to allowing the rear end portions 11b of the movable contactors 11 to be inserted therebetween. The rear end portions 11b of the movable contactors 11 and the extending portions 18a of the terminal base 18 are in contact with each other such that they can be electrically connected. In order for the rear end portions 11b of the movable contactors 11 and the extending portions 18a of the terminal base 18 to be in contact with each other stably, the rear end portions 11b of the movable contactors 11 and the extending portions 18a of the terminal base 18 are in contact with each other in a state of being inserted in an accommodation space for their mutual contact, and a Belleville spring (which is also called a Belleville washer) (not shown) or a wave washer (not shown) are inserted between the rear end portions 11b of the movable contactors 11 and the extending portions 18a of the terminal base 18 in order to provide an elastic force to the extending portion 18a of the terminal base 18 so that the extending portion 18a can be brought into contact with the rear end portions 11b of the movable contactors 11.
However, the movable contact assembly for the current limiting type MCCB as described above has a structure in which the extending portions 18a, which have a poor flexibility, are pushed to be brought into contact with the rear end portions 11b of the movable contactors 11 by the Belleville washer or the wave washer, and in this case, because the contact area between the extending portions 18a of the terminal base 18 and the rear end portions 11b of the movable contactors 11 is narrow and has a high contact resistance, making a loss of electric power transmission.
Also, in the movable contactor assembly for the current limiting type MCCB, the configuration of the spring mechanism for applying elastic force for the contact pressure of the movable contactors includes three springs 14, three spring support pins 15 and three rollers 17, and the coupling means (spring sheets, a pin connection extending plate, a roller support pin) of the rollers 17 and the spring support pins 15, and the spring holder 13 are all installed within the holder 12, and because there are so many components, the assembling productivity is degraded.
In addition, in the movable contactor assembly for the current limiting type MCCB, the spring support pins 15 are formed to be elongate, they must be formed through being cut by a lathe in order to satisfy the strength tolerating the elastic force of the springs 14. Thus, much time is taken to fabricate the spring support pins 15 and the fabrication cost is increased.